31 ANIMAL MECHANISM. 



cylinder be maintained, the curves retain the same form so 

 long as the muscle gives the same movements. 



Not only are shocks produced iu the muscle by acting 

 upon its nerve by electricity, but also by applying electric 

 excitement to the muscle itself. Pinching, percussion, and 

 cauterization of the nerve are also excitants which provoke 

 shocks of the muscle. 



The character of these movements changes under certain in- 

 fluences. Fatigue of the muscle, the cooling of that organ, the 

 stoppage of circulation in its interior, modify the form of the 

 shock, diminish its force, and augment its duration. Under 

 these influences the myographic curve passes through different 

 forms, such as 1, 2, 3, Fig. 4. 



Fir.. 4. Character of the shnck, according to the dearree of fttjgiie of the 

 muscle : 1, muscle fresh ; ~2, muscle a httlu fatigued; 3, musclo still mure 

 fatigued. 



Among the different species of animals, the durations of the 

 shock vary considerably ; in the bird they are very brief (two 

 to three hundredth?) of a second). In man they are longer ; 

 in- the tortoise and hyberuating animals longer still. Certain 

 poisons modify the characteristics of this movement in so 

 special a manner, that the slightest traces of those poisons 

 introduced into the circulation of the animal may be disco- 

 vered in the form of the tracings. 



By Fig. 5, we may judge of the successive forms which 

 will be assumed by the shocks of the muscle of a frog, under 

 the influence of a gradual absorption of vcratrine. 



These experiments still reveal only one fact: it is that 

 the muscle is shortened or lengthened by a movement whose 



